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. 2021 Mar 24;11:6780. doi: 10.1038/s41598-021-86094-5

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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Hydraulic-fracture design at depth of 410 m at Äspö HRL, Sweden. (a) A hydraulic-testing borehole (diameter: 102 mm; length: 28 m) is diamond-drilled subparallel to the minimum horizontal stress. The hydraulic fracture (disk) opens perpendicular to the minimum principal stress and rapidly grows in the plane of intermediate (vertical) and maximum principal stress (horizontal). (b) Photograph of pulse-fatigue hydraulic-fracturing-packer system as it is inserted into the horizontal-injection borehole. (c) Geometry of injection borehole with six injection intervals (HF1–HF6) and inclined monitoring boreholes (diameter: 76 mm; length: up to 30 m), which are equipped with 70-kHz AE sensors (cones).